The present invention relates to an apparatus and a method for separating particles from hot gases.
The present invention particularly relates to a centrifugal separator assembly, which may be connected to a reactor, such as a combustor or gasifier, for separating solid particles discharged with flue gases from its reactor chamber. The peripheral walls of the centrifugal separator's vortex chamber delimit an interior gas volume with at least one gas vortex therein. A first wall portion of the peripheral walls includes an inlet for introducing the flue gases and solid particles entrained therein into the vortex chamber. The vortex chamber further includes at least one gas outlet, for discharging purified gas therefrom, and at least one particles outlet, for discharging separated solid particles therefrom.
The present invention more particularly relates to centrifugal separator assemblies, which are suitable for separating solid particles from process or product gases in fluidized bex reactors, such as circulating fluidized bed reactors used for combustion or gasification of carbonaceous or other fuels.
Conventional centrifugal separators have cyclones delimited by cylindrical peripheral walls and a conical bottom. It has, however, recently been noticed that centrifugal separators can advantageously be made also of planar wall panels, the vortex chamber formed thereby having a non-circular horizontal cross section. U.S. Pat. No. 5,281,398 discloses this kind of a centrifugal separator, according to which particles entrained in hot gases are separated in a vortex chamber delimited by a plurality of substantially planar plates or panels, the vortex chamber having a polygonal, preferably quadrate, horizontal cross section. Such a separator has numerous especially cost saving advantages over conventional centrifugal separators, it is particularly easy to construct, even if made of water tube panels, and it may easily be integrated with reactor furnaces made of similar wall panels, thereby providing a compact overall design. Gas is introduced into the non-circular vortex chamber, through a gas inlet in the side wall thereof, so as to guide the gas as tangentially as possible into the gas vortex formed within the vortex chamber, in order to maximize the swirling or spinning of the gas in the gas vortex.
The advantages of introducing gas tangentially into the vortex chamber is well-known, also in conventional cylindrical cyclones. This advantage has also been noticed in U.S. Pat. No. 5,070,822 suggesting a centrifugal separator having its vortex chamber centrally located within the upper most part of a cylindrical furnace. The centrifugal separator comprises a plurality of wing-like elements arranged one after the other on the upper periphery of the vortex chamber. A plurality of spaced gas inlets is thus formed between the wing-like elements along the entire periphery of the vortex chamber. The wing-like elements, which may be made of a ceramic material, are directed so as to guide the plurality of gas flows through the inlets tangentially into a vortex formed centrally within the vortex chamber.
In a centrifugal separator with planar walls, as disclosed in earlier mentioned U.S. Pat. No. 5,281,398, the inlet to the separator is a vertical slot located so as to lead the gas flow and the solid particles therein as tangentially as possible towards the vertical gas vortex formed within the vortex chamber. A simple opening in a side wall of the vortex chamber does, however, have a rather poor guiding effect on the gas and solid particles flowing into the vortex chamber. A considerable portion of the gas and solid particles introduced through the opening immediately deviates from the intended tangential direction and meets the gas vortex at an angle substantially greater than zero. This to some extent decreases the swirling velocity of the gas vortex and lowers the separation efficiency of the system. Some of the solid particles may also, if not directed correctly, hit the walls of the vortex chamber at an unfavorable angle, thereby causing heavy erosion.
It has been suggested to insert vertical guide plates around the inlet opening in order to increase the horizontal directionality of the gas and solid particle stream, in order to force the gas and solid particles to flow into the vortex chamber in the intended direction. The guide plates form an inlet duct which has to be rather long, in order for the duct to have a real impact on the direction of movement of the gas and solid particle stream introduced into the vortex chamber.
The long guide plates or guiding walls are located within the vortex chamber for achieving the desired effect. Such inserts within a vortex chamber have, however, to be very well supported, insulated and protected in order to endure in the hot surroundings. Large extra constructions are heavy and have to be well supported and they also have to be connected firmly so as not to vibrate and decrease strength of the overall construction. To insert large elements, as suggested, into the vortex chamber goes against the general trend in the manufacturing of particle separators, which is to avoid the addition of any extra elements, which take space, have to be supported and protected. There is a need to make an as simple, straightforward and self-supporting construction as possible.
Further, it has been noticed in non-circular centrifugal separators, closely integrated with the reactor furnace, i.e., being connected by a common wall thereto, and having elements therein forming two or more gas vortices within the vortex chamber, that the strength of the common wall between the separator and the reactor furnace, especially the strength to withstand pressure differences between the furnace and the separator, is an important factor. The common wall tends to vibrate unless supported. It has, therefore, been suggested to dispose in the vortex chamber a partition or supporting wall, extending from the common wall to the opposite wall between two gas vortices, in order to increase the strength and suppress vibration. Such a supporting wall, however, also constitutes a rather large extra element within the vortex chamber, which preferably should be avoided.
Non-circular vortex chambers and reactor furnaces may also be built non-integrated, i.e., without a common wall, and mechanically connected to each other only through a distinct inlet duct. This prevents the pressure difference between the reactor chamber and the vortex chamber from directly having an impact on a wall in the vortex chamber. An inlet duct, if long enough, may further have a positive impact on directionality, i.e., it may help to lead the gas and solid particles tangentially into the gas vortex within the vortex chamber. The non-integrated construction requires, however, a lot of space and gives rise to a considerable increase in the costs.
There is obviously a need for new solutions, particularly in centrifugal separators with planar walls, to improve the directionality or orientation of the stream of gas and particles entering a centrifugal separator, i.e., to introduce the stream of gas and particles into the vortex chamber of the centrifugal separator without the stream being immediately spread or scattered, or without causing turbulence in the stream. The desire is to keep together the stream. This should, however, be done with inserts having a limited length, i.e., inserts which do not protrude so deep into the vortex chamber that they have a negative impact on the gas vortex therein. Such new solutions should preferably also be cost effective and able to improve the strength of the structure without requiring additional space in the vortex chamber.